1. Field of the Invention
This invention relates to a cable condition monitoring device configured to monitor a damaged condition of a cable.
2. Description of the Related Art
In case of a cable that is wired in a place to which fluctuation and flection are applied, breaking of a conductor part and cracking of an insulating material part may be caused due to repeated flexing fatigue, and there is a possibility that disconnection of electric power signal or electric signal to be transmitted, formation of short circuit to ground or the like is caused.
In particular, in case of a cable that is used for power supply or signal transmission to an industrial robot or the like, the cable is wired in a severe environment for the cable, thus it is needed to more strictly prevent defects due to the breaking and the short circuit.
Incidentally, if cracks occur in the insulating material part of the cable, stress at the time of flection may be concentrated in the area of the cracks so as to allow the conductor part to be early broken by fatigue. In addition, if cracks occur in the insulating material part, it is considered that insulation between the conductor part and the surrounding part thereof may become insufficient, for example, the conductor part and a shield conductor may form a short circuit so as to lead to a serious accident. Consequently, it is important to constantly monitor an occurrence of cracks in the insulating material part, namely a damaged condition of the insulating material part during flection operation so as to ensure reliability of the whole system.
As a technique that is capable of constantly monitoring the damaged condition of the insulating material part, there is a technical idea disclosed in, for example, JP-A-2003-001433.
The cable damage detection device disclosed in JP-A-2003-001433 is configured such that an enclosed gas is enclosed in a gas layer formed between a conductor part and an insulating material part of a cable so as to detect whether the enclosed gas is decreased in pressure or not by a pressure gauge. If damages such as cracks occur in the insulating material part, gases flow out from the area of cracks, and the enclosed gas is decreased in pressure, so as to make it possible to constantly monitor the damages of the insulating material part by monitoring the pressure of the enclosed gas.